arch/powerpc/lib/locks.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Spin and read/write lock operations.
   4  *
   5  * Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
   6  * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
   7  * Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
   8  *   Rework to support virtual processors
   9  */
  10
  11 #include <linux/kernel.h>
  12 #include <linux/spinlock.h>
  13 #include <linux/export.h>
  14 #include <linux/smp.h>
  15
  16 /* waiting for a spinlock... */
  17 #if defined(CONFIG_PPC_SPLPAR)
  18 #include <asm/hvcall.h>
  19 #include <asm/smp.h>
  20
  21 void splpar_spin_yield(arch_spinlock_t *lock)
  22 {
  23         unsigned int lock_value, holder_cpu, yield_count;
  24
  25         lock_value = lock->slock;
  26         if (lock_value == 0)
  27                 return;
  28         holder_cpu = lock_value & 0xffff;
  29         BUG_ON(holder_cpu >= NR_CPUS);
  30
  31         yield_count = yield_count_of(holder_cpu);
  32         if ((yield_count & 1) == 0)
  33                 return;         /* virtual cpu is currently running */
  34         rmb();
  35         if (lock->slock != lock_value)
  36                 return;         /* something has changed */
  37         yield_to_preempted(holder_cpu, yield_count);
  38 }
  39 EXPORT_SYMBOL_GPL(splpar_spin_yield);
  40
  41 /*
  42  * Waiting for a read lock or a write lock on a rwlock...
  43  * This turns out to be the same for read and write locks, since
  44  * we only know the holder if it is write-locked.
  45  */
  46 void splpar_rw_yield(arch_rwlock_t *rw)
  47 {
  48         int lock_value;
  49         unsigned int holder_cpu, yield_count;
  50
  51         lock_value = rw->lock;
  52         if (lock_value >= 0)
  53                 return;         /* no write lock at present */
  54         holder_cpu = lock_value & 0xffff;
  55         BUG_ON(holder_cpu >= NR_CPUS);
  56
  57         yield_count = yield_count_of(holder_cpu);
  58         if ((yield_count & 1) == 0)
  59                 return;         /* virtual cpu is currently running */
  60         rmb();
  61         if (rw->lock != lock_value)
  62                 return;         /* something has changed */
  63         yield_to_preempted(holder_cpu, yield_count);
  64 }
  65 #endif